TOI-261.01
Astrophysical Synthesis & Habitability Characterization
TOI-261.01 is a confirmed sub-neptune exoplanet orbiting the star TOI-261, located approximately 373.4 light-years (114.5 parsecs) from the Solar System. First announced in 2021 by Transiting Exoplanet Survey Satellite (TESS) using the Transit detection technique (producing an estimated primary transit depth of 0.0476% across the stellar disk), this world measures 3.045 Earth radii (0.27 Jupiter radii) and has a measured mass of 9.51 Earth masses. Combining its mass and radius yields a mean bulk density of 1.86 g/cm³ (a low bulk density dominated by an extended hydrogen-helium gaseous envelope), a surface gravity of 1.03 g⊕ (10.1 m/s²), and an escape velocity of 19.8 km/s.
In its orbital architecture around TOI-261, TOI-261.01 completes one full revolution every 3.364 Earth days at a semi-major axis of 0.034792 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 112.5 km/s (compared to Earth's 29.8 km/s).
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 1722 K (+1449°C / +2640°F) and receiving 874.80 S⊕ (~1,190,597 W/m²), TOI-261.01 orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star TOI-261 is classified as a stellar host with an effective photospheric temperature of 5,890 K, a radius of 1.2802 R☉, a mass of 0.4967 M☉, an estimated bolometric luminosity of 1.77 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = -0.35 dex (metal-poor relative to the Sun). From Earth, TOI-261 shines at apparent V-band magnitude 9.56 (accessible to binoculars and small amateur telescopes) in the Southern celestial hemisphere. The TOI-261 system is a multi-planet architecture hosting 2 confirmed worlds, with TOI-261.01 sharing its stellar neighborhood alongside TOI-261.02.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Transiting Exoplanet Survey Satellite (TESS) · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | TOI-261 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,890 K |
| Stellar Radius | 1.2802 R☉ |
| Stellar Mass | 0.4967 M☉ |
| Bolometric Luminosity | 1.77 L☉ |
| Metallicity [Fe/H] | -0.350 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.560 · G: 9.423 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.034792 AU |
| Orbital Period | 3.364 days |
| Mean Orbital Velocity | 112.5 km/s |
| Orbital Eccentricity (e) | Circular (0.00) |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 1.86 g/cm³ (19.8 km/s vesc) |
| Insolation Flux | 874.7956 S⊕ (~1,190,597 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 373.400 LY (114.495 pc) |